VOYEUR: Fix logical bug related to the computer data and positioning
FULLPIPE: Implement sceneHandler18and19_showManJump()
FULLPIPE: Implement sceneHandler18and19_boyJumpTo()
FULLPIPE: Implement sceneHandler19_updateNumRides()
AVALANCHE: Implement MainMenu::wait().

Rework other pieces of the engine to fit to it's mechanism.
VOYEUR: Rename some computer fields
AVALANACHE: Rework use of MainMenu.
AVALANCHE: Rework use of ShootEmUp.